A frequency band or an operating frequency band may support a specific duplex mode of operation. Examples of possible duplex modes are: frequency division duplex (FDD), time division duplex (TDD) and half duplex FDD (HD-FDD).
In frequency division duplex (FDD) mode of operation, which is used in Universal Terrestrial Radio Access Network (UTRAN) FDD and Evolved Universal Terrestrial Radio Access Network (E-UTRAN) FDD, the uplink and downlink transmission take place on different carrier frequency channels. Therefore, in FDD mode both uplink and downlink transmission can occur simultaneously in time. On the other hand in time division duplex (TDD) mode, which is used in UTRAN TDD and E-UTRAN TDD, the uplink and downlink transmission take place on the same carrier frequency channel but in different time slots or sub-frames. Half duplex FDD (HD-FDD) that is used in Global System for Mobile communications (GSM) can be regarded as a hybrid scheme where the uplink and downlink are transmitted on different carrier frequencies and are also transmitted on different time slots. This means that uplink and downlink transmission do not occur simultaneously in time.
One primary objective of the standardization of next generation of mobile telecommunications systems in 3rd Generation Partnership Project (3GPP) is to develop a frequency band, which can preferably be used globally or at least in large number of countries. A global or regional band leads to several advantages in terms of global roaming, reduced cost of the products due to the economy of scale, simplicity in building products/devices since the same or at least limited platforms/devices can be reused globally or regionally etc. However certain country specific and even operator specific frequency bands are unavoidable due to the fact that the spectrum availability for the mobile services may be fragmented in different countries and even within a country. Furthermore, the regulators in each country independently allocate the frequency band in accordance with the available spectrum. Also the spectrum below 1 GHz, due to its very promising propagation characteristics, might be scarce or fragmented due to higher demand by other competing technologies. Hence there might be several smaller frequency bands even in the same frequency range allocated in different parts of the world. These local or operator specific bands may partially overlap or may be adjacent in frequency. The assigned spectrum will eventually be standardized in 3GPP in terms of frequency bands so that vendors can develop the products e.g. base stations and user equipments. The standardization of a frequency band encompasses various aspects including the band numbering, raster, carrier frequency channel numbering, user equipment and base station radio requirements, user equipment and base station performance requirements, Radio Resource Management (RRM) requirements etc.
For example, several bands are standardized and allocated in various parts of the world in 800 MHz range for UTRAN FDD and E-UTRAN FDD e.g. bands 5, 6, 18 and 19. Some of the individual frequency bands within 800 MHz range are shown in FIG. 1a-1d. In band 5, which is used in America, Australia and a few countries in Asia and illustrated in FIG. 1a, 824-849 MHz 10a is allocated for uplink and 869-894 MHz 11a is allocated for downlink. In band 6, which is used in Japan and illustrated in FIG. 1b, 830-840 MHz 10b is allocated for uplink and 875-885 MHz 11b is allocated for downlink. In band 18, which is also used in Japan, operator specific and illustrated in FIG. 1c, 815-830 MHz 10c is allocated for uplink and 860-875 MHz 11c is allocated for downlink. In band 19, which is also used in Japan, operator specific and illustrated in FIG. 1d, 830-845 MHz 10d is allocated for uplink and 875-890 MHz 11d is allocated for downlink.
It can be observed from FIG. 1a-1d that either these bands overlap or are adjacent. Secondly most of them are country or even operator specific. Therefore in 3GPP there has been an extensive effort to develop one or two harmonized frequency bands in the 800 MHz range, which could cover all or most of the bands within this frequency range.
The term ‘harmonized band’ stems from the fact that it is the super-set or that it covers more than one smaller or individual frequency band in the frequency range. Examples of possible harmonized bands in the 800 MHz range are shown in FIGS. 2a-2b. In the example of a harmonized band currently studied in 3GPP and illustrated in FIG. 2a, 814-849 MHz 20a is allocated for uplink and 859-894 MHz 21a is allocated for downlink. In another example of a harmonized band currently studied in 3GPP and illustrated in FIG. 2b, 806-849 MHz 20b is allocated for uplink and 859-894 MHz 21b is allocated for downlink. The harmonized bands in FIGS. 2a and 2b cover all the frequency bands illustrated in FIG. 1a-1d. 
The user equipment/terminal capable of supporting a harmonized band should be able to operate in several of these specific or individual bands. This will lead to lower user equipment costs since specific hardware for an individual band in this range, e.g. 800 MHz, is not required. Furthermore, all operators holding spectrum in the same frequency range would be able to easily get sufficient terminals facilitating their network operation. The terminals supporting the harmonized band must also be compliant to the regulatory requirements in the legacy bands in order to operate in these.
The harmonization of frequency bands is possible in any frequency range, which contains more than one smaller or fragment bands e.g. in 1900 MHz range. Another frequency range being considered for the harmonization is 700 MHz, which is currently fragmented into several smaller operator specific bands.
In order to simplify the frequency search or the so-called initial cell search the center frequency of a radio channel is specified to be an integral multiple of a well defined, generally fixed number, called channel raster. This enables the user equipment to tune its local oscillator only at one of the raster points assuming it to be the center frequency of the channel being searched.
The channel raster in UTRAN FDD is 200 KHz but for certain channels and bands it is also 100 KHz. In E-UTRAN FDD and TDD channel raster for all channels, i.e. all bandwidths, is 100 KHz. The channel raster directly impacts the channel numbering, which is described in the following.
The carrier frequencies in a frequency band are enumerated. The enumeration is standardized such that the combination of the frequency band and the carrier frequency can be determined by a unique number called absolute radio frequency number. In GSM, UTRAN and E-UTRAN the channel numbers are called Absolute Radio Frequency Channel Number (ARFCN), UTRA Absolute Radio Frequency Channel Number (UARFCN) and E-UTRA Absolute Radio Frequency Channel Number (EARFCN), respectively.
In FDD systems separate channel numbers are specified for uplink (UL) and downlink (DL). In TDD there is only one channel number since the same frequency is used in both directions.
The channel numbers, e.g. EARFCN, for each band are unique in order to distinguish between different bands. The channel number for each band can be derived from the expressions and mapping tables defined in the relevant specifications. Based on the signalled channel numbers, e.g. EARFCN in E-UTRAN, and the pre-defined parameters associated with each band the user equipment can determine the actual carrier frequency in MHz and the corresponding frequency band. This is explained by the following example.
For example the relation between the EARFCN and the carrier frequency FDL in MHz for the downlink is pre-defined by the following equation:FDL=FDL_low+0.1(NDL−NOffs-DL)Where FDL_low and NOffs-DL are pre-defined values for each band and NDL is the downlink EARFCN.
Consider E-UTRAN band 5, whose EARFCN range NDL lies between 2400-2649 MHz. The pre-defined values of FDL_low and NOffs-DL are 869 MHz and 2400 MHz, respectively. Assume that the network signals that downlink EARFCN is 2500 MHz. Using the above expression the user equipment can determine that the downlink carrier frequency of the channel is 879 MHz. Furthermore as stated above, the pre-defined EARFCN range is unique for each band. Hence, the user equipment can determine the frequency band corresponding to the signalled EARFCN. An expression to derive the E-UTRAN FDD uplink carrier frequency, which is similar to that of the downlink carrier frequency, is also pre-defined. In E-UTRAN FDD both fixed transmit-receive frequency separation, i.e. fixed duplex, and variable transmit-receive frequency separation, i.e. variable duplex, are supported. If fixed transmit-receive frequency separation is used by the network then the network does not have to signal the uplink EARFCN since the user equipment can determine the uplink carrier frequency from the downlink carrier frequency and the pre-defined duplex gap. In case the variable duplex is employed by the network for a certain band then both downlink and uplink EARFCN have to be signalled.
For the initial cell search or more specifically for the initial carrier frequency search the user equipment has to search at all possible raster frequencies e.g. with 100 KHz resolution in the E-UTRAN frequency band. However, for the user equipments camped on or connected to the cell, the network signals the absolute radio frequency channel number(s) for performing measurements, mobility decisions such as cell reselection or commanding handover to certain cell belonging to certain frequency channel of the same or of a different radio access technology (RAT) etc. Hence, the user equipment can, after camping on a cell in idle mode or when connected to a cell in connected mode, acquire the cell specific or user equipment specific system information, which contains the absolute radio frequency channel number(s).
The network can request the user equipment to perform handover to a cell operating on another carrier frequency i.e. an inter-frequency handover or to a cell belonging to another RAT i.e. an inter-RAT handover. The inter-frequency or inter-RAT handover is performed to a cell on a carrier frequency, which may or may not belong to the frequency band of the serving cell. In both handover scenarios, the carrier frequencies of the serving cell and the target cells are different. Therefore, in order to assist the UE to perform the inter-frequency or inter-RAT handover the network signals the frequency channel number of the target carrier frequency in the handover command.
According to state of the art solutions the user equipment supporting a harmonized frequency band, which overlaps with one or more individual smaller legacy frequency bands, will implement the carrier frequency channel numbers and other relevant information related to the harmonized band, which harmonized band is denoted HB.
In the past UTRAN FDD and E-UTRAN FDD band 6 used in Japan was extended by 5 MHz. The new extended UTRAN FDD and E-UTRAN FDD band 6 is called UTRAN FDD and E-UTRAN FDD band 19. Hence band 19, which is the super-set of band 6, can be regarded as the harmonized band with respect to band 6. The entire band 19 is country specific. It has therefore been specified that band 6 is not applicable. This means that the network will only implement band 19. This solution as used for bands 6/19 is not possible for a harmonized band, which overlaps with several individual bands in several countries and an individual band may also be owned by more than one operator. Thus, it is not likely that all operators using the individual band would refarm their legacy network to the new harmonized band.
Individual bands overlapping with the harmonized band, e.g. in the 800 MHz range, will exist in various parts of the world. This is because the frequency assignment in different parts of the world may be different and therefore it is not likely that all networks in different parts of the world will implement the new harmonized band. However, there will be several user equipments capable of supporting the harmonized band as this will reduce the cost and avoid the need for user equipments with separate implemented hardware for each individual band. However, a user equipment supporting the harmonized band will not be able to recognize relevant information of the smaller legacy bands. Furthermore, a user equipment, which is capable of supporting a harmonized band HB, entering in a network using future smaller individual bands SB will not be able to recognize relevant information of the future smaller individual bands.